(a) Technical Field
The present invention relates to a method for manufacturing an electrode of a dye-sensitized solar cell using an inkjet printing process, an electrode formed thereby, and a dye-sensitized solar cell having the electrode. More particularly, it relates to a method for manufacturing an electrode of a dye-sensitized solar cell module wherein a thin metal electrode is formed using an inkjet printing process, and wherein a transparent conductive film coating is provided to protect the metal electrode.
(b) Background Art
Generally, dye-sensitized solar cells include a working electrode coated with TiO2 including Ru-based dye capable of absorbing light on a transparent electrode, a counter electrode coated with platinum, and an I−/I3− based electrolyte disposed between the working electrode and the counter electrode.
Recently, much research has been conducted on dye-sensitized solar cells due to their relatively low manufacturing cost, transparent electrodes, and presence of various designs. However, typical dye-sensitized solar cells are disadvantageous in that the photoelectric conversion efficiency rapidly decreases as the unit area of the dye-sensitized solar cell increases. In an attempt to address the above limitation, studies are being extensively conducted to enhance the photoelectric conversion efficiency by reducing the resistance through formation of a metal electrode on a transparent substrate.
Dye-sensitized solar cells require a protective layer to protect a metal electrode from the electrolyte because such cells use liquid electrolyte.
Glass frit has been widely used as a protective layer, but it has a limitation because the electrolyte penetrates into the glass frit to oxidize the metal electrode and reduce the photoelectric conversion efficiency and durability. In other words, typical dye-sensitized solar cells still have a limitation of corrosion of an electrode. Thus, various methods are being studied in attempt to overcome this limitation.
According to one of the various methods, a metal electrode is first formed by a typical screen printing method on a flat or curved glass substrate or a glass substrate coated with a barrier layer, and then a transparent conductive layer is formed thereon. The barrier layer prevents sodium ions (Na+) contained in glass components, such as SiO2, from passing through to the transparent conductive film and/or improves adhesive property between the surface of the glass substrate and the transparent conductive film.
In this case, the metal electrode can be directly fabricated on the substrate without requiring disposition of a specific barrier layer between the substrate and metal electrode. In case of soda-lime glass, since conductive film coating is difficult due to sodium ions (Na+) escaping from the glass components during the conductive film coating, a barrier layer is first formed.
Also, in cases where the surface of a glass substrate is rough, a barrier layer may be introduced to improve the state of the glass surface. Accordingly, the adhesion and uniformity of the conductive film can be improved during the formation of the transparent conductive film.
The above method for forming the electrode of the dye-sensitized solar cell advantageously improves durability by protecting the metal electrode with the transparent conductive film.
A typical screen printing method may be used for forming a metal electrode. The metal electrode formed by the screen printing method has a thickness of about 5 μm or higher, often about 10 μm. Further, the transparent conductive film generally has a thickness of about 500 nm to 1 μm. Therefore, it is necessary to considerably reduce the thickness of the metal electrode so that it can be adequately protected from liquid electrolyte. In other words, although a metal electrode needs to be protected from liquid electrolyte during the formation of the electrode of the typical dye-sensitized solar cell, since the transparent conductive film having a thickness of about 1 μm is much thinner than the metal electrode having a thickness of at least 5 μm, it is difficult to protect the metal electrode from liquid electrolyte.
In an attempt to increase the area of the dye-sensitized solar cell and improve reduction of the photoelectric conversion efficiency in manufacturing a module thereof, there has been proposed a method in which a lithography process is used to etch a portion of a line where a metal electrode is formed by a thickness of the metal electrode. Then a metal is filled into the etched portion through electroplating or electrolessplating, and then a conductive film is formed thereon. However, this method is not advantageous because a process for manufacturing a mask for etching the substrate is required, and expensive equipment is further required.
There has been proposed another method in which a metal electrode is thinly formed by sputtering, chemical vapor deposition, and electrolessplating processes. This method includes forming a pattern using photolithography or E-beam lithography processes to form a metal electrode, followed by forming a metal mesh layer through etching. When a resist pattern is first coated on a substrate, and then irradiated by UV through a mask of a pattern to be manufactured, a light receiving portion undergoes a change in its chemical structure and dissolves in a developer solution. A metal electrode is coated/deposited on the dissolved portion, and then the resist pattern of the other portion is removed. Since this method includes an additional process of etching a metal electrode after a mask manufacturing process, the manufacturing process is complicated. Further, a large amount of compounds are used during the mask manufacturing process and the etching process, and samples may be contaminated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.